U.S. Pat. No. 2,835,711 (Wolfe et al.) discloses a batch process for reacting fluorides of Group IIA elements of the Periodic Table with carbon to form fluorocarbons which have a variety of utilities, including as intermediates for conversion to tetrafluoroethylene. Only details for high melting Group IIA metal fluorides are given and these involve the melting of the metal fluoride in a crucible by using a carbon arc. Powdered carbon can also be mixed with the metal fluoride in the crucible and the carbon electrodes immersed in the resultant mixture. Gaseous fluorocarbons, primarily CF.sub.4, evolve from the resultant melt, leaving behind the reaction product between the metal of the metal fluoride and carbon, which is identified as CaC.sub.2 in Example 1.
U.S. Pat. No. 2,709,191 (Farlow et al.) discloses the reaction of silicon fluoride with carbon to produce tetrafluoroethylene at extremely low conversions of the silicon fluoride per pass (Example II) and obtaining increasing proportions of CF.sub.4 instead of tetrafluoroethylene at multiple passes (Example I). The "pass" in the process is the passage of silicon fluoride gas at a slow rate through the burning arc struck between two graphite electrodes, and then the gas (reaction product and unreacted silicon fluoride) flows through the hollow bore of one of the electrodes. The carbon reactant of the process comes from the consumable carbon electrode, although carbon powder can also be flowed through the arc with the silicon fluoride. Various operating pressures are disclosed but low pressure (1 to 150 mm of mercury) is disclosed to be preferable. Argon can be used to set the operating pressure, which is then maintained by the silicon fluoride feed. The gaseous reaction mixture is quenched to a temperature no higher than 400.degree. C. within 0.001 to 0.1 sec.
U.S. Pat. No. 2,852,574 (Denison et al.) discloses the pyrolysis of certain Group VA and VIA elements as fluorides or certain organic fluorides to decompose the gaseous fluoride feed at temperatures greater than 1700.degree. C. The pyrolysis is preferably carried out at pressures less than 300 mm Hg by passing the gaseous fluoride starting material through an electric arc struck between carbon electrodes, one of which has a hollow bore, whereby the carbon from the electrodes becomes consumed by combining with the fluorine to form fluorocarbon radicals. The fluorocarbon radicals are passed through the bore of the hollow electrode to contact carbon particles which are at a temperature below 500.degree. C., which quenches the fluorocarbon radicals to favor the formation of TFE over CF.sub.4. CF.sub.4, however, is disclosed to be a preferred organic fluoride. Together with the TFE and CF.sub.4 present in the product stream, the byproducts of the Group VA and VI fluorides are also in gaseous form at room temperature.
The Farlow process has never achieved commercial exploitation for the manufacture of tetrafluoroethylene (TFE) because of the low conversion and low yield giving a generally low production rate of this product. Although Denison achieved higher yields, this process suffered from such problems as difficulty in control of the pyrolysis process by virtue of the electrodes being consumed and low production rate, and thus, this process never achieved commercial exploitation. Instead, TFE has been made commercially worldwide by an entirely different process since the 1950's by a series of process steps, involving (i) reaction of CaF.sub.2 with H.sub.2 SO.sub.4 to form HF, (ii) synthesis of chloroform, (iii) reaction of HF with chloroform to form chlorodifluoromethane (HCFC-22), and (iv) pyrolysis of HCFC-22 to form TFE, and refining the TFE. This series of processes starts with a reactant used in the Wolfe process, but then proceeds on a journey involving the building of four plants ((i) to (iv) above) to arrive at the reaction product of the Farlow process at a high production rate, nevertheless making the manufacture of TFE very expensive, and creating a large amount of HCI byproduct for further processing or disposal.
There has existed a long-felt need for the ability to produce tetrafluoroethylene more economically.